1. Field of the Invention
The present invention relates to a steel tube having aluminum fins wound helically thereon. More particularly, this invention relates to an improved form of finned tube and the method of making the same.
2. Prior Art
In the heat exchange art, one conventional exchange unit consists of a cylindrical steel tube upon which a thin aluminum fin is helically would or attached. In order for the heat exchange unit to operate effectively, it is necessary that there be a heat-conductive union between the tubular body and the helical fin.
However, one problem arises from the fact that steel and aluminum have different coefficients of thermal expansion. That is, if the aluminum fin is tightly wound around the steel tube at ambient temperatures, the fin will expand away from the tube when the elements are heated; thus, bringing the fin out of contact with the tube so that the fin will be unable to conduct heat away from the tube.
One prior art proposal to obviate the above noted problem, is to provide a helical groove or recess in the tube and to wind the aluminum fin in the groove. If the groove is properly sized as to width and depth, the fin will still remain in contact with the tube even though it expands outwardly in the groove.
A patentability search was conducted on the present invention and the following listed U. S. Patents were uncovered in the search.
______________________________________ U.S. Pat. No. Inventor Date ______________________________________ 877,252 Stolp 1-21-08 2,152,331 Shoemaker 3-28-39 2,182,238 Rasmussen 12-05-39 2,268,680 Von Linde 1-06-42 2,270,810 Larriva 1-20-42 2,310,970 Limpert 2-16-43 2,379,879 Bronander 7-10-45 2,396,795 Lea 3-19-46 2,453,448 McTurk 11-09-48 2,252,092 Bruegger 10-10-50 ______________________________________
The closest patent appears to be the Shoemaker Pat. No. 2,152,331, which shows, in FIG. 3, a fin 11 helically wound around a tube 10. Elements 12 and 13 are described as stabilizing strands. In FIG. 3 of the Shoemaker patent, the strands are triangular in cross section; in FIG. 6, they are square; in FIG. 8 they are round. On page 2, column 1, lines 30-32, it is stated that the stabilizing strands can be of any other suitable cross section. In the Shoemaker patent, the stabilizing strands are fastened to the tube by a bath of solder or by brazing the ends to the tube. In no event, however, does the Shoemaker patent teach or suggest the simultaneous wrapping of the fin and the stabilizing strands. Furthermore, the Shoemaker patent does not show or suggest the feature of simultaneously winding a fin and a wire to provide an alternate contiguous relationship.